OK, I'll bite. If we don't have gasoline or natural gas, and we don't
use hydrogen, what will be powering the world, and by extension, my
E-T? ;-)

Well, my answer should be, read the book.
Powering the world is a rather complex subject. Takes a few chapters.

However, taking your E-T for starters, that's about electricity. If we
don't have natural gas, then hydrogen would likely come from electricity
(via electrolysis). But you will be much better off charging directly
from the grid than having electricity converted to hydrogen (60-70%
efficient on commercial scale), then transported, then converted back to
electricity (less than 50% efficient, best case). Instead of getting
100% of the original kWhs, you would get about 30%, after two
conversions and transport losses (ignoring storage losses). That's just
one issue.

I'd also like to hear your views on Amory Lovins' Winning the Oil
Endgame...., which as I'm sure you know strongly argues for hydrogen as
the primary fuel, with solar/wind/etc in secondary roles. It's dense
with financial and technical calculations and seems to make a strong
case that hydrogen IS feasible.

Hydrogen IS technically feasible. The hydrogen industry has been around
for a century. The hydrogen economy is just a really bad idea.

As others have already noted, hydrogen as a fuel is an energy carrier,
not a primary energy source (or fuel). However, it's not a very good
one. It's not energy dense - even liquid hydrogen only stores about 25%
of the energy of gasoline by volume. Liquid hydrogen and pressurized
hydrogen bring new issues to handling relative to fuels that are liquid
at ambient temperatures (e.g., gasoline, ethanol, methanol, diesel fuel,
vegetable oil).

I have given up on chasing Amory Lovins regarding hydrogen since the
Hypercar was corrupted to the hydrogen hype, and the debate over the
Twenty Hydrogen Myths paper. I suspect, as with so many other things
regarding hydrogen lately, with the right assumptions, you can reach the
desired conclusion.